1. Field of the Invention
The present invention relates to medical connectors and infusion sets.
2. Brief Description of the Related Art
In general, whenever a therapeutic fluid is to be delivered subcutaneously to a patient form an external source, a passageway, such as that provided by a hollow needle or other type of cannula or catheter device, must be first inserted through the skin of the patient in order to provide a passageway or channel through which the fluid may pass from its source external to the patient to the desired subcutaneous location under the skin of the patient. Once this passageway has been installed, the desired infusion system may be used in conjunction with an appropriate catheter connecting the external source of fluid with the passageway leading to the subcutaneous delivery point to deliver the fluid to the patient at an appropriate delivery rate.
Unfortunately, several problems associated with infusing fluids into the patient as described above are usually encountered. Most systems require the patient to use a syringe that is fitted with a thread or luer fitting. The patient must fill the syringe and attach the catheter to it. However, in doing so the medication can become contaminated and is therefore no longer sterile. Non-sterile solutions can lead to infection. In addition the inconvenience of having to fill the syringe in the first place, and then attach and prime the catheter is difficult for many patients.
In the early 1990""s prefilled insulin cartridges were first introduced by insulin manufacturing companies for use in insulin pens. These cartridges are prefilled and make their use very convenient for the patient. The difficulty is that the prefilled cartridges need to have a septum to allow the medication to remain sterile.
The recent popularity of insulin infusion pumps as an alternative to multiple daily injections for insulin-dependent diabetics requires the use of such an injection set to deliver insulin from a small, portable insulin infusion pump to the subcutaneous injection location. However, these devices require the patient to fill a syringe, which defeats the sterility of the mixture. Furthermore, there exists a substantial problem with the use of injection sets, as described above, in that flexible PVC is not completely insulin-compatible. This is in contrast to hard PVC, which is safe for use with insulin. While the exact nature of the reaction exhibited by insulin in contact with flexible PVC has not been determined with certainty, it is believed that the insulin, which is pH sensitive, reacts with CO2, the flow of which therethrough is not inhibited by flexible PVC. In addition, the large quantities of plasticizer used in flexible PVC may result in a leaching problem when used with insulin.
Since flexible PVC is not a barrier for CO2, the CO2 which flows through the flexible PVC tubing will react with the insulin, causing the insulin to aggregate and to precipitate out of solution. Such precipitation of the insulin will likely cause clotting and blockage in the tube or in the needle, thereby inhibiting the flow of insulin to the subcutaneous depot.
Heat will also accelerate the clotting process of insulin in flexible PVC tubing without the pH change caused by CO2. The reason for this has not been finally determined, but it may be due to zinc in the insulin forming zinc chloride. In any event, heat will further compound the situation faced by delivery of insulin through flexible PVC tubing.
The amount of insulin exiting the injection set will therefore vary considerably, with portions of the insulin becoming attached to the interior of the tube and eventually coating the interior of the tube, even if blockage does not occur. Over time, the situation will improve somewhat assuming blockage of the tube per se does not occur, but the amount of insulin actually delivered to the patient will vary considerable even with the best of circumstances. It may therefore be appreciated that the use of a flexible PVC tubing injection set to deliver insulin from an insulin infusion pump is neither desirable nor medically acceptable.
Other substances exhibit reactions when delivered through flexible PVC tubing. Lipids and proteins have adverse reactions with flexible PVC delivery systems, and nitroglycerin also reacts to some degree with a flexible PVC environment.
One solution which has been proposed to the problem has been through the use of polyethylene tubing, which does not cause a reaction with insulin passing therethrough. Polyethylene is a barrier to CO2, and the major problem of CO2 passing through the tubing is thereby eliminated. Additionally, the problem of clotting of the insulin due to heat is also substantially minimized.
Several problems have arisen with the use of epoxy bonded polyethylene infusion sets, all of which are due to the relative disadvantage of the epoxy bonding process to a solvent bonding process. First of all, an epoxy bond is simply not as strong as a solvent bond. Secondly, epoxy bonds have substantial aging problems, which limit shelf life of the injection set. Since the epoxy bond loses its mechanical bonding properties over time, the injection set will become less sturdy, with the potential for the tubing coming loose from the needle increasing substantially over time. Thirdly, batch control of epoxy used in epoxy bonding is time consuming and cumbersome. Finally, epoxy bonding or xe2x80x9cpottingxe2x80x9d is a more expensive process than solvent bonding, resulting in a product having an economic disadvantage relative to a product made by solvent bonding.
It is thereby apparent that there exists a substantial need for an injection set for delivery of insulin (or other fluids exhibiting reactions when flowed through flexible PVC tubing), which injection set utilizes polyethylene tubing to inhibit reaction and subsequent degradation of insulin flowing therethrough.
According to a first exemplary embodiment, a medication infusion set comprises a base tube having an exterior surface, a proximal end, a distal end, and an inner lumen extending between the proximal and distal ends, the base tube formed of a material selected from the group consisting of polyethylene and polypropylene, a rigid cannula having a proximal end, a distal end, and a lumen extending between the proximal and distal ends, the cannula proximal end positioned in the base tube lumen, and a tube of a heat shrinkable material positioned on the base tube exterior surface at least in a region of the base tube in which the cannula is inserted, the heat shrinkable tube having been heat shrunk to the exterior of the base tube and compressing the base tube and the cannula together to form a seal.
According to a second exemplary embodiment, an infusion device comprises a housing including a proximal end, a distal end, two lateral sides, and a bore extending between the proximal end and the distal end, a soft cannula having a proximal end, a distal end, and a lumen extending between the proximal end and the distal end, the cannula positioned in part in the housing bore with the cannula distal end outside of the housing, and a locking device attached to a lateral side of the housing, the locking device including a locking finger and a lever, the lever extending distally and the locking finger extending proximally, the locking finger including a distally facing surface.
According to a third exemplary embodiment, a connecting device comprises a hub including a proximal end face, a distal end face, two lateral sides, and a bore extending between the proximal end and the distal end, rigid cannula including a proximal end, a distal end, and a lumen extending between the proximal end and the distal end, the rigid cannula mounted in the hub bore with the rigid cannula distal end exterior of the hub, a pin extending distally from the hub distal end face and offset laterally from the rigid cannula, and a proximally facing surface on one of the lateral sides positioned between the proximal end face and the distal end face.
According to a fourth exemplary embodiment, a process of forming a medical infusion set comprises the steps of inserting an end of a rigid cannula into the lumen of a length of tubing, and heat shrinking a tube of heat shrinkable material over the portion of the tubing in which the end of the rigid cannula is positioned to compress the tubing onto the rigid cannula.